Evolution of Oxygen-Ion and Proton Conductivity in Ca-Doped Ln2Zr2O7 (Ln = Sm, Gd), Located Near Pyrochlore-Fluorite Phase Boundary.

Sm2-xCaxZr2O7-x/2 (x = 0, 0.05, 0.1) and Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore-fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 °C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100-900 °C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700-950 °C. The Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 °C, and pure oxygen-ion conductivity above 700 °C. The 500 °C proton conductivity contribution of Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) is ~ 1 × 10-4 S/cm. The fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 °C. As a result, of the morphotropic phase transition from pyrochlore Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) to fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2-xCax)Zr2O7-δ (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2-xCaxZr2O7-x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice.

Proton and oxygen ion conductivity in the pyrochlore/fluorite family of Ln2-xCaxScMO7-δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1) niobates and tantalates.

The tolerance factor is a good criterion to understand the structural transitions in Ln2-xCaxScMO7-δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1). Decreasing the Ln ionic radius in Ln2ScNb(Ta)O7 leads to a morphotropic transition from a pyrochlore to a fluorite-like structure. Ca2+-doping leads to a pyrochlore-to-fluorite transition in Ln2-xCaxScMO7-δ (Ln = La, Sm) and a fluorite-to-pyrochlore transition in Ho2-xCaxScNbO7-δ. Proton contribution to the total conductivity was observed for Ln2-xCaxScNb(Ta)O7-δ (Ln = La, Sm; x = 0, 0.05, 0.1) 3+/5+ pyrochlores and the maximum proton contribution was shown by Sm1.9Ca0.1ScMO6.95 (M = Nb, Ta), which are located at the boundary between pyrochlores and fluorites (comparative study of electrical conduction and oxygen diffusion). Proton conduction of Sm1.9Ca0.1ScNbO6.95 and Sm1.9Ca0.1ScTaO6.95 pyrochlores persists up to 800 and 850 °C, respectively. The conductivity of fluorite-like Ho2-xCaxScNbO7-δ (x = 0, 0.05) and Yb2ScNbO7 is dominated by the oxygen ion transport, in accordance with their energy activation values 1.09-1.19 eV. The dielectric permittivity and TG studies were used for the investigation of oxygen vacancy dynamics and water incorporation into the Ln2-xCaxScNb(Ta)O7-δ (Ln = La, Sm, Ho, Yb; x = 0, 0.05, 0.1) lattice. It is shown that oxygen vacancy-related dielectric relaxation in the range of 550-650 °C (ambient air), typical of pyrochlores and fluorites with pure oxygen ion conductivity, decreases and disappears for proton-conducting oxides.

Culturing of Mouse Mesenchymal Stem Cells on Poly-3-Hydroxybutyrate Scaffolds.

We studied the possibility of long-term culturing of mouse mesenchymal stem cells on a porous scaffold made of biocompatible polymer poly-3-hydroxybutyrate. The cells remained viable for at least 2 months and passed more than 65 population doublings in culture. Culturing on the scaffold did not change surface phenotype of cells. 3D poly-3-hydroxybutyrate scaffolds are appropriate substrate for long-term culturing of mesenchymal stem cells.

Phase transition in single crystal Cs2Nb4O11.

We studied temperature dependence of complex capacitance, impedance, and polarized Raman spectra of single crystal Cs2Nb4O11. First, we observed a sharp lambda-shaped peak at 165 degrees C in the complex capacitance, then found drastic changes in the Raman spectra in the same temperature range. Utilizing the pseudosymmetry search of structure space group, we attributed the observed anomalies to a structural change from the room temperature orthorhombic Pnn2 to another orthorhombic Imm2. We also measured room temperature polarized Raman spectra in different symmetries of normal vibrations and assigned high wavenumber Raman bands to the internal vibrations of NbO6 octahedra and NbO4 tetrahedra.